1. Technical Field
This invention relates to a color-coded target, a color code extracting device, and a three-dimensional measuring system. More specifically, this invention relates to a color-coded target having codes with the colors thereof chosen so as not to cause code reading errors, a color code extracting device for automatically detecting the codes, and a three-dimensional measuring system for measuring three-dimensional coordinates using the color code extracting device.
2. Related Art
The three-dimensional image measurement is a method of determining three-dimensional coordinates of an object to be measured using images taken from different directions. In such a method, an identification work is required to determine the same position in a number of images taken from different directions. When the number of images taken increases, there arises a problem that the amount of manual identification work becomes great and the work takes much time. Therefore, the inventors have developed a color-coded target and a technique for automatically detecting and processing the target with an intention of automating the conventional manual work and improving the efficiency of identification process in measuring three-dimensional images. (Refer to Patent Documents 1 and 2.)
The color-coded target is a code target, for example a rectangular sheet, with retro-targets at its three corners for discriminating a code by the combination of color disposition in the color code area. Employing code targets using colors makes it possible to increase the number of codes by increasing the number of colors. In the process of detecting the color-coded target, first the retro-targets at three corners are detected and a color-coded target area is determined. Next, the color of the color-coded area is extracted and the extracted color is processed to be converted into a code value. Finally, a label using the conversion-processed code value related to the position detected with the retro-target is affixed to the color-coded target. This has made it possible to automate the identification work and the work has been greatly improved in efficiency. In particular, the work efficiency has been remarkably improved in three-dimensional measurement of objects with a large number of points to be measured.    [Patent Document 1] JP-A-2007-64627 (paragraphs 0025-0145, FIGS. 1-24)    [Patent Document 2] JP-A-2007-101277 (paragraphs 0024-0074, FIGS. 1-20)
However, a problem has been left unsolved on how to choose the color of the color-coded target. If a color code is read incorrectly and as a result a wrong position is determined to be an identical position for the target position, a great amount of time is required to find out the incorrectly determined position and correct it. Therefore, it is important to choose colors so as not to cause such an error.
The object of this invention is to provide a color-coded target with a color code of colors chosen not to cause code reading errors, and a technique for automatically detecting and processing the color-coded target.